U.S. patent application number 09/855663 was filed with the patent office on 2002-05-02 for functional film.
This patent application is currently assigned to TDK Corporation. Invention is credited to Iijima, Tadayoshi, Kawahara, Hiroshi, Takasugi, Yasufumi, Tamai, Kiminori.
Application Number | 20020051879 09/855663 |
Document ID | / |
Family ID | 18654846 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020051879 |
Kind Code |
A1 |
Tamai, Kiminori ; et
al. |
May 2, 2002 |
Functional film
Abstract
An object of the present invention is to provide functional
films which can exhibit a variety of functions using functional
fine particles, in particular, a transparent conductive film having
a low resistance value using conductive fine particles. The
functional film of the present invention is a functional film
comprising a support and a functional layer on at least one surface
of the support, wherein the above functional layer contains
functional fine particles, and a ratio (.sigma.1/.sigma.2) between
a dispersion value (.sigma.2) obtainable from the alignment of the
functional fine particles at the front surface of the functional
layer and a dispersion value (.sigma.1) obtainable from the
alignment of the functional fine particles at the opposite surface
of the functional layer is from 1.2 to 1.85. Thereby, a sufficient
contact of the functional fine particles is effected in the
functional layer and the strength of the functional layer and the
adhesiveness between the functional layer and the support become
large, so that a transparent conductive film wherein conductive
fine particles are used as the functional fine particles, for
example, has a low electric resistance.
Inventors: |
Tamai, Kiminori; (Chuo-ku,
JP) ; Iijima, Tadayoshi; (Chuo-ku, JP) ;
Kawahara, Hiroshi; (Chuo-ku, JP) ; Takasugi,
Yasufumi; (Chuo-ku, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
TDK Corporation
1-13-1, Nihonbashi
Chuo-ku
JP
|
Family ID: |
18654846 |
Appl. No.: |
09/855663 |
Filed: |
May 16, 2001 |
Current U.S.
Class: |
428/336 ;
428/328; 428/421 |
Current CPC
Class: |
C23C 24/00 20130101;
Y10T 428/3154 20150401; Y10T 428/256 20150115; G02B 1/10 20130101;
Y10T 428/24942 20150115; Y10T 428/25 20150115; H01B 1/20 20130101;
Y10T 428/257 20150115; Y10T 428/265 20150115 |
Class at
Publication: |
428/336 ;
428/328; 428/421 |
International
Class: |
B32B 005/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 19, 2000 |
JP |
2000-148904 |
Claims
What is claimed is:
1. A functional film comprising a support and a functional layer on
at least one surface of the support, wherein the above functional
layer contains functional fine particles, and a ratio
(.sigma.1/.sigma.2) between a dispersion value (.sigma.2)
obtainable from the alignment of the functional fine particles at
the front surface of the functional layer and a dispersion value
(.sigma.1) obtainable from the alignment of the functional fine
particles at the opposite surface of the functional layer is from
1.2 to 1.85.
2. The functional film according to claim 1, wherein the above
support is a transparent resin film.
3. The functional film according to claim 1, wherein the above
functional fine particles are conductive fine particles.
4. The functional film according to claim 3, wherein average
primary particle size of the above conductive fine particles is in
the range of 5 to 50 nm.
5. The functional film according to claim 3, wherein the thickness
of the above functional layer is in the range of 0.5 to 5
.mu.m.
6. The functional film according to claim 3, wherein the above
functional layer contains a resin in an amount of the range of 3.7
by volume or less when the volume of the above conductive fine
particles is regarded as 100.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a functional film. In the
present invention, the functional film is defined as follows. That
is, the functional film means a film having a function, and the
function means an action exhibited through a physical and/or
chemical phenomenon. The functional film includes films having
various functions such as a conductive film, a magnetic film, a
ferromagnetic film, a dielectric film, a ferroelectric film, an
electrochromic film, an electroluminescence film, an insulating
film, a light-absorption film, a light-selective-absorption film, a
reflection film, an antireflection film, a catalyst film, and a
photocatalyst film.
[0002] In particular, the present invention relates to a
transparent conductive film. The transparent conductive film can be
used as a transparent electrode such as an electrode for an
electroluminescence panel, an electrode for an electrochromic
device, an electrode for a liquid crystal display, a transparent
planar heating element, or a touch panel, and also as a transparent
electromagnetic wave-shielding film.
[0003] Heretofore, functional films comprising a variety of
functional materials have been produced by a physical vapor
deposition (PVD) such as vacuum deposition, laser-abrasion,
sputtering, or ion plating, or a chemical vapor deposition (CVD)
such as thermal CVD, light CVD, or plasma CVD. These methods
generally require huge facilities and some of them are not suitable
for the formation of a film of a large area.
[0004] Furthermore, the film formation by coating using a sol-gel
method is also known. The sol-gel method is also suitable for the
formation of a film having a large area, but in most cases, it is
necessary to sinter an inorganic material at a high temperature
after the coating.
[0005] For example, the production of the transparent conductive
film is as follows. Currently, the transparent conductive film is
mainly produced by a sputtering method. There are a variety of
sputtering procedures. One example is a method of forming a
transparent conductive layer by acceleration-bombarding inert gas
ions generated by direct current or high-frequency discharge in
vacuum to a target surface, beating the atoms constituting the
target out of the surface, and depositing them onto a support
surface.
[0006] The sputtering method is advantageous because a transparent
conductive film having a low surface electric resistance can be
formed even when the film is large to some degree. However, the
method has defects that the apparatus is large and the film
formation is slow. When a transparent conductive film having a
larger area is required in future, the apparatus should be larger.
This requirement results in the necessity of enhanced accuracy on
control as a technical problem, and also results in the problem of
increase of production cost in another aspect. Furthermore, for
compensating the slow film formation, the formation is accelerated
by increasing the number of the target, but the increase is
problematic because it also makes the apparatus larger.
[0007] The production of the transparent conductive film is also
attempted by an coating method. A conventional coating method
comprises applying a conductive coating composition, wherein
conductive fine particles are dispersed in a binder solution, onto
a resin film, and drying and hardening the composition to form a
transparent conductive film. The coating method is advantageous
because a transparent conductive film having a large area can be
easily formed, the apparatus is simple, productivity is high, and
the transparent conductive film can be produced at a cost lower
than that in the sputtering method. In the transparent conductive
film formed by the coating method, conductivity is expressed by the
formation of an electric pathway owing to the mutual contact of the
conductive fine particles. However, the transparent conductive film
prepared by the conventional coating method has a defect that the
contact of the conductive fine particles is insufficient owing to
the presence of the binder and thus the resulting transparent
conductive film has a high electric resistance (inferior
conductivity), so that the use is limited.
[0008] As a production of a transparent conductive film by the
conventional coating method, Japanese Patent Application Laid-Open
No. 109259/1997 discloses a process for producing the film
comprising a first step of forming a conductive layer by applying a
coating composition comprising conductive powder and a binder resin
onto a plastic film for transcription and drying the coated film, a
second step of pressing the surface of the conductive layer to a
smooth plane (5 to 100 kg/cm.sup.2) and heating the surface (70 to
180.degree. C.), and a third step of laminating the conductive
layer on a plastic film or sheet and fixing them by applying
pressure under heating.
[0009] In this method, a conductive film having a low electric
resistance is not obtained because of the use of a large amount of
the binder resin (100 to 500 parts by weight of conductive powder
relative to 100 parts of the binder in the case of inorganic
conductive powder; 0.1 to 30 parts by weight of conductive powder
relative to 100 parts of the binder in the case of organic
conductive powder).
[0010] Further, Japanese Patent Application Laid-Open No.
199096/1996 discloses a method of applying a coating composition
for forming a transparent conductive film comprising tin-doped
indium oxide (ITO) powder, a solvent, a coupling agent, and an
organic or inorganic acid salt of a metal but containing no binder
onto a glass plate, and sintering it at a temperature of
300.degree. C. or higher. In this method, the electric resistance
of the conductive film is low because of no use of binder. However,
since it is necessary to conduct the sintering step at a
temperature of 300.degree. C. or higher, it is difficult to form a
conductive film on a support such as a resin film. That is, a resin
film is melted, carbonized, or fired at the high temperature. The
temperature limit may depend on the kind of the resin films and,
for example, it may be 130.degree. C. for polyethylene
terephthalate (PET) film.
[0011] As a conductive film formed by other method than the coating
method, Japanese Patent Application Laid-Open No. 13785/1994
discloses a conductive film comprising a powder-compressed layer
where at least part of, preferably all of the voids of skeleton
structure constituted by conductive material (metal or alloy)
powder are filled with a resin, and a resin layer present under the
layer. The method of the production will be explained by
exemplifying the case of forming a film on a plate material.
According to the above patent publication, a resin, a powdery
material (metal or alloy) and a plate material which is a member to
be treated are first shaken or stirred in a vessel together with a
film-forming medium (steel balls having a diameter of several
millimeter) to form a resin layer on the surface of the member to
be treated. Successively, the powdery material is trapped and fixed
in the resin layer by the adhesive action of the resin layer.
Further, the film-forming medium shaken or stirred imparts an
impact force to the powdery material shaken or stirred to form a
powder-compressed layer. However, for obtaining a fixing effect of
the powder-compressed layer, a considerable amount of the resin is
required. Moreover, the process is more complicated than the case
of the coating method.
[0012] As another conductive film formed by a method other than the
coating method, Japanese Patent Application Laid-Open No.
107195/1997 discloses a conductive fiber-resin integrated layer
obtained by depositing a conductive short fiber on a film of PVC
and the like through sprinkling the fiber, followed by
pressurization. The conductive short fiber is a short fiber such as
polyethylene terephthalate subjected to a covering treatment such
as nickel plating. The pressurizing operation is, however,
preferably conducted under a temperature condition at which the
resin matrix layer shows thermoplasticity and thus, conditions of a
high temperature and a low pressure such as 175.degree. C. and 20
kg/cm.sup.2 are required, so that it is difficult to form a
conductive film on a support such as a resin film.
[0013] In consideration of such circumstances, it is desired to
develop a functional film capable of forming easily a film having a
large area, which can be prepared using a simple apparatus with
high productivity and low cost, as well as has a high quality.
[0014] In particular, for a conductive film, it is desired to
develop a conductive film capable of forming easily a film having a
large area, which can be prepared using a simple apparatus with
high productivity and low cost, as well as has a high quality.
SUMMARY OF THE INVENTION
[0015] An object of the present invention is to provide functional
films which can exhibit a variety of functions using functional
fine particles.
[0016] In particular, an object of the present invention is to
provide a conductive film having a low resistance value using
functional fine particles.
[0017] For achieving such an object, the functional film of the
present invention is constituted by a functional film comprising a
support and a functional layer on at least one surface of the
support, wherein the above functional layer contains functional
fine particles, and a ratio (.sigma.1/.sigma.2) between a
dispersion value (.sigma.2) obtainable from the alignment of the
functional fine particles at the front surface of the functional
layer and a dispersion value (.sigma.1) obtainable from the
alignment of the functional fine particles at the opposite surface
of the functional layer is from 1.2 to 1.85.
[0018] As a preferred aspect of the functional film, it has a
constitution wherein the above support is a transparent resin
film.
[0019] As a preferred aspect of the functional film, it has a
constitution wherein the above functional fine particles are
conductive fine particles.
[0020] As a preferred aspect of the functional film, it has a
constitution wherein average primary particle size of the above
conductive fine particles is in the range of 5 to 50 nm.
[0021] As a preferred aspect of the functional film, it has a
constitution wherein the thickness of the above functional layer is
in the range of 0.5 to 5 .mu.m.
[0022] Further, as a preferred aspect of the functional film, it
has a constitution wherein the above functional layer contains a
resin in an amount of the range of 3.7 by volume or less when the
volume of the above conductive fine particles is regarded as
100.
[0023] According to the present invention as above, the functional
film comprising a functional layer on at least one surface of a
support is a film wherein the above functional layer contains
functional fine particles, and a ratio (.sigma.1/.sigma.2) between
a dispersion value (.sigma.2) obtainable from the alignment of the
functional fine particles at the front surface of the functional
layer and a dispersion value (.sigma.1) obtainable from the
alignment of the functional fine particles at the opposite surface
of the functional layer is 1.2 or more, so that a sufficient
contact of the functional fine particles is effected in the
functional layer and therefore, the strength of the functional
layer and the adhesiveness between the functional layer and the
support become large. Accordingly, a transparent conductive film
wherein conductive fine particles are used as the functional fine
particles, for example, has a low electric resistance. Moreover,
the adhesiveness between the support and the functional layer is
strong enough to use it for a long period of time. Furthermore, it
is also possible to use a transparent support such as a transparent
resin film as the support, and the functional film of the present
invention can be formed as a film having a large area by changing a
coating apparatus or a compressing apparatus.
BRIEF EXPLANATION OF THE DRAWINGS
[0024] FIG. 1 is a drawing illustrating one example of a cross
sectional photograph of 100 thousand magnifications of a
transparent conductive film which is one embodiment of the
functional film of the present invention.
[0025] FIG. 2 is a drawing for the explanation of the procedure for
obtaining the dispersion values, .sigma.1, .sigma.2, from the lines
showing the alignments of the conductive fine particles at the
front surface and the opposite surface of a transparent conductive
layer.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] The following will explain modes for carrying out the
present invention.
[0027] The functional film of the present invention is a functional
film comprising a functional layer on at least one surface of a
support, wherein the functional layer contains functional fine
particles, and a ratio (.sigma.1/.sigma.2) between a dispersion
value (.sigma.2) obtainable from the alignment of the functional
fine particles at the front surface of the functional layer and a
dispersion value (.sigma.1) obtainable from the alignment of the
functional fine particles at the opposite surface of the functional
layer is from 1.2 to 1.85.
[0028] The following will explain the present invention by
exemplifying a transparent conductive film which is one embodiment
of the functional film of the invention. By the way, in the present
invention, "transparent" means to transmit a visible light. The
level of the degree of light scattering required varies with the
applications of the transparent conductive film.
[0029] The transparent conductive film which is a functional film
of the present invention comprises a transparent conductive layer
as the functional layer on a transparent support.
[0030] The transparent conductive layer constituting the
transparent conductive film contains conductive fine particles as
the functional fine particles, and a ratio (.sigma.1/.sigma.2)
between a dispersion value (.sigma.2) obtainable from the alignment
of the functional fine particles at the front surface of the
transparent conductive layer and a dispersion value (.sigma.1)
obtainable from the alignment of the functional fine particles at
the opposite surface of the transparent conductive layer is from
1.2 to 1.85. In the present invention, the above dispersion values
.sigma.1 and .sigma.2 are defined as follows. That is, the
alignment of the conductive fine particles at the opposite side of
the front surface of the transparent conductive layer at the cross
sectional photograph of 100 thousand magnifications of the
transparent conductive film and the alignment of the conductive
fine particles at the front side are each traced. For the resulting
two kinds of lines showing aligning states of the conductive fine
particles, the distance from a base line was measured at plural
points and the average squares of differences between the average
of the measured values and each measured value are defined as
.sigma.1 and .sigma.2.
[0031] This requirement will be explained in detail with reference
to FIGS. 1 and 2. First, a squared tracing paper is placed on the
cross sectional photograph of 100 thousand magnifications of the
transparent conductive film (FIG. 1) without deviation, and the end
surface at which the conductive fine particles at the opposite side
(Side 1A in FIG. 2) of the front surface of the transparent
conductive layer are aligned and the end surface at which the
conductive fine particles at the front side (Side 1B in FIG. 2) of
the transparent conductive layer are aligned are each traced to
obtain lines L1 and L2 showing aligning states of the conductive
fine particles. By the way, since the part where the conductive
fine particles are apparently lacked affects the measurement, a
line segment is obtained at the lacking part by extrapolating from
both side of the lacking part. Then, base line B1 and B2 are drawn
at about 1 cm apart from each of the lines L1 and L2 showing
aligning states of the conductive fine particles. And, the
distances between the base line B1 and the line L1 showing an
aligning state of the conductive fine particles are measured at an
interval of 1 to 2 mm (the measuring length are 10 cm or more), and
the average square of the differences between the average value of
the measured values and each measured value is defined as the
dispersion value .sigma.1. Similarly, the distances between the
base line B2 and the line L2 showing an aligning state of the
conductive fine particles are measured at an interval of 1 to 2 mm,
and the average square of the differences between the average value
of the measured values and each measured value is defined as the
dispersion value .sigma.2. Thereafter, the ratio
(.sigma.1/.sigma.2) of the dispersion value .sigma.1 to the
dispersion value .sigma.2 is calculated.
[0032] The transparent conductive layer which has the ratio
(.sigma.1/.sigma.2) of the dispersion value .sigma.1 to the
dispersion value .sigma.2 of 1.2 to 1.85 is realized only at the
state wherein the constituting conductive fine particles are
embedded in the transparent support. In the conventional
transparent conductive films, the opposite side of the transparent
conductive layer are smooth surfaces which directly reflect the
smooth surface of the transparent support, and there is no
transparent conductive layer having the ratio (.sigma.1/.sigma.2)
of 1.2 or more. When the ratio (.sigma.1/.sigma.2) is less than
1.2, the mutual contact of the conductive fine particles becomes
insufficient and it is difficult to obtain a transparent conductive
layer excellent in conductivity. Moreover, the strength of the
transparent conductive layer is low and the adhesiveness to the
transparent support becomes also insufficient. On the other hand,
though higher ratio of .sigma.1/.sigma.2 is preferred, a high
compressing force is required in the formation of the transparent
conductive layer and thus pressure resistance of the compressing
apparatus should be raised, so that the ratio up to 1.85 is
generally suitable.
[0033] As the conductive fine particles constituting the above
transparent conductive layer, known inorganic conductive fine
particles can be used without limitation unless they impair the
transparency of the transparent conductive film.
[0034] The inorganic conductive fine particles includes tin oxide,
indium oxide, zinc oxide, cadmium oxide, and the like, and fine
particles of antimony-doped tin oxide (ATO), fluorine-doped tin
oxide (FTO), tin-doped indium oxide (ITO), aluminum-doped zinc
oxide (AZO), and the like are preferred. Further preferred is ITO
because it results in more excellent conductivity. Alternatively,
those obtained by coating the surface of the fine particles having
transparency such as barium sulfate with an inorganic material such
as ATO or ITO can be also used.
[0035] The average primary particle size of these conductive fine
particles is 300 nm or less, preferably 100 nm or less, more
preferably in the range of 5 to 50 nm. When the average primary
particle size of the conductive fine particles exceeds 300 nm,
there is a high possibility that the balance of properties of the
transparent conductive layer is impaired, and thus the case is not
preferred.
[0036] The thickness of the transparent conductive layer comprising
the above conductive fine particles may be in the range of 0.1 to
10 .mu.m, preferably 0.5 to 5 .mu.m. The electric resistance of the
transparent conductive layer can be optionally determined depending
on the applications of the transparent conductive film.
[0037] In the present invention, the transparent conductive layer
constituting the transparent conductive film may contain a minute
amount of a resin unless it increases the electric resistance. For
example, when the volume of the above conductive fine particles is
regarded as 100, the resin can be incorporated to the transparent
conductive layer in an amount of less than 25, preferably less than
20, more preferably 3.7, by volume. More preferred is to
incorporate no resin to the transparent conductive layer. The resin
has a function of reducing light scattering but causes an increase
of the electric resistance of the transparent conductive film. This
is because the mutual contact of the conductive fine particles is
inhibited by the insulating resin and, in the case of a large
amount of the resin, the conductive fine particles do not come into
contact with each other, so that the electron transfer among the
fine particles is inhibited. Accordingly, in consideration of the
improving haze degree and securing the conductivity among the
conductive fine particles, the resin may be used within the above
volume range, if incorporated. Within the range of the resin
amount, the amount of the resin is small and thus, most of the
resin is considered to exist in the void of the conductive fine
particles.
[0038] As the above resin, thermoplastic resins or polymers having
a rubber elasticity excellent in transparency can be used solely or
in combination of two or more without limitation. Examples of the
resin include fluorine polymers, silicone resins, acrylic resins,
polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl
cellulose, regenerated cellulose diacetyl cellulose, polyvinyl
chloride, polyvinyl pyrrolidone, polyethylene, polypropylene, SBR,
polybutadiene, polyethylene oxide, and the like.
[0039] The fluorine polymers include polytetrafluoroethylene,
polyvinylidene fluoride (PVDF), vinylidene fluoride-ethylene
trifluoride copolymer, ethylene-tetrafluoroethylene copolymer,
propylene-tetrafluoroethylene copolymer, and the like. In addition,
fluorine-containing polymers obtainable by substituting the
hydrogen of the main chain with an alkyl group may be also used.
The larger the density of the resin is, the easier it is to satisfy
the above volume requirement, since the volume is smaller even when
a large weight of the resin is used.
[0040] By the way, the volume of the above conductive fine
particles and the volume of the resin are not apparent volumes but
real volumes. Real volume is determined by determining density
using an instrument such as pycnometer in accordance with JIS Z
8807 and dividing the weight of the material to be used by the
density. The reason why the amount of the resin to be used is
defined by not the weight but the volume is because the situation
is more clearly reflected when it is considered how the resin
exists relative to the conductive fine particles in the transparent
conductive layer.
[0041] As the transparent support constituting the transparent
conductive film of the present invention, a variety of materials
such as a resin film and glass can be used. Thereby, the
transparent conductive layer is well adhered to the transparent
support as if part of the conductive fine particles which are into
contact with the transparent support are embedded in the
transparent support. In the case that a material having a larger
hardness than that of the conductive fine particles, e.g., a
material having a large hardness such as glass or a rein film
having a hard surface, is used as the transparent support, a
transparent support where a resin layer having a smaller hardness
than that of the conductive fine particles is formed beforehand on
the hard glass surface or hard film surface is used. Thereby, the
conductive fine particles are embedded in the resin layer, and thus
the adhesiveness between the transparent conductive layer and the
transparent support becomes sufficient.
[0042] By the way, after the formation of the transparent
conductive layer, the resin layer having a small hardness may be
hardened by heat or ultraviolet ray. The resin layer is preferably
a substance which is not dissolved in the liquid in which the
conductive fine particles are dispersed. When the resin is
dissolved, the solution containing the above resin comes periphery
of the conductive fine particles by capillary action, and as a
result, the electric resistance increases. Also, after the
formation of the transparent conductive layer, the resin layer can
be peeled off the glass surface or the hard film surface to form a
transparent conductive film comprising a transparent resin layer as
the transparent support.
[0043] The above resin layer may be formed by one or two or more of
thermoplastic resins or polymers having a rubber elasticity
excellent in transparency. Examples of the resin include fluorine
polymers, silicone resins, acrylic resins, polyvinyl alcohol,
carboxymethyl cellulose, hydroxypropyl cellulose, regenerated
cellulose diacetyl cellulose, polyvinyl chloride, polyvinyl
pyrrolidone, polyethylene, polypropylene, SBR, polybutadiene,
polyethylene oxide, and the like.
[0044] In the case of using a non-flexible material such as glass
or ceramic, attention should be paid because there is a high
possibility that the material may be broken during the process.
Therefore, the transparent support is preferably a resin film which
is not broken. The resin film is also preferable, as mentioned
below, in view of the good adhesion to the transparent conductive
layer comprising the conductive fine particles and is suitable for
the applications wherein weight saving is required. Accordingly, in
the case that the use at a high temperature is not intended, the
resin film can be used as the transparent support.
[0045] Examples of the resin film include films of polyesters such
as polyethylene terephthalate (PET), films of polyolefins such as
polyethylene and polypropylene, polycarbonate films, acrylic films,
norbornene film (Arton manufactured by JSR K.K.), and the like.
[0046] By the way, the transparent support having haze of the range
of 0.5 to 5% can be used depending on the applications.
[0047] In the present invention, it is also possible to form a
transparent conductive film comprising transparent conductive
layers at both surfaces of a transparent support.
[0048] The next will explain one example of the method for
producing the transparent conductive film of the present
invention.
[0049] The transparent conductive layer constituting the
transparent conductive film can be formed by applying a dispersion
containing conductive fine particles and optional minute amount of
a resin as a conductive coating composition onto a transparent
support and drying the whole, followed by compression.
[0050] As a liquid for dispersing the conductive fine particles, in
the case that the conductive coating composition contains a resin,
known various solvents can be used without limitation as far as the
resin is dissolved in the solvents. Examples of the solvents
include saturated hydrocarbons such as hexane; aromatic
hydrocarbons such as toluene and xylene, alcohols such as methanol,
ethanol, propanol, and butanol; ketones such as acetone, methyl
ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; esters
such as ethyl acetate and butyl acetate; ethers such as
tetrahydrofuran, dioxane, and diethyl ether; amides such as
N,N-dimethylformamide, N-methylpyrrolidone (NMP), and
N,N-diemthylacetamide; halogenated hydrocarbons such as ethylene
chloride and chlorobenzene; and the like. Among them, polar
solvents are preferred, and alcohols such as methanol and ethanol
and amides such as NMP are suitable. These solvents can be used
solely or in combination of two or more. Furthermore, a dispersing
agent may be used for improving the dispersibility of the
conductive fine particles.
[0051] Moreover, water is also usable as the solvent. In the case
of using water, the transparent support should be hydrophilic. The
above resin layer or resin film is usually hydrophobic and thus
tends to repel water, so that it is difficult to obtain a uniform
film. In the case that the surface of the transparent support
comprises a resin layer, or in the case that the transparent
support is a resin film, it is necessary to mix water with an
alcohol, or to make the surface of the support hydrophilic. By the
way, when the conductive coating composition contains a resin, it
is preferable to consider the solubility of the resin, too.
[0052] The amount of the solvent to be used is not particularly
limited and may be determined so that the dispersion of the
conductive fine particles has a viscosity suitable for coating. For
example, relative to 100 parts by weight of the conductive fine
particles, the amount may be about 100 to 100000 parts by weight of
liquid. The amount of the solvent may be optionally selected
depending on the kinds of the conductive fine particles and the
liquid.
[0053] The dispersing of the conductive fine particles into the
liquid can be conducted by a known dispersing method. For example,
they are dispersed by sand grinder mill process. At the dispersion,
it is also preferable to use media such as zirconia beads for
raveling agglomerated conductive fine particles. At the dispersion,
attention should be paid so that the contamination of impurities
such as dust does not occur.
[0054] The dispersion of the above conductive fine particles may be
blended with various additives within the range where the
conductivity is not decreased. Examples thereof include additives
such as UV absorber, surfactant, and dispersing agent.
[0055] The dispersion of the conductive fine particles can be
applied onto the transparent support by a known method without
particular limitation. For example, it can be effected by coating
methods such as reverse roll method, direct roll method, blade
method, knife method, extrusion nozzle method, curtain method,
gravure roll method, bar coat method, dipping method, kiss coat
method, and squeeze method. In addition, the dispersion can be
attached onto the transparent support by atomization, spraying, and
the like.
[0056] The drying temperature varies depending on the kind of the
liquid used for the dispersion, but is preferably from about
10.degree. C. to about 150.degree. C. When the temperature is lower
than 10.degree. C., the moisture in the air tends to condense and
at higher than 150.degree. C., the resin film support is deformed.
Moreover, attention should be paid so that impurities do not attach
to the surface of the conductive fine particles at drying.
[0057] The thickness of the conductive fine particles-containing
layer after coating and drying depends on the compressing
conditions of the next step and the applications of the transparent
conductive film, but may be from about 0.1 .mu.m to about 10
.mu.m.
[0058] As mentioned above, a uniform film is easily prepared by
dispersing the conductive fine particles in the liquid, applying
the dispersion and drying. When the dispersion of the conductive
fine particles is applied and dried, the fine particles form a film
even when a large amount of binder resin as in a conventional
method is not present in the dispersion, that is, the resin is not
incorporated or the amount of the resin is less than a specific
amount as in the present invention. The reason why a film is formed
even under absence of a large amount of the binder resin is not
exactly clear, but it is considered that the fine particles is
gathered by capillary action when the amount of the liquid becomes
small through drying, and the fine particles have a large specific
surface area and a strong cohesive force, thereby the film being
formed. However, the film at this stage has the ratio
(.sigma.1/.sigma.2) of the dispersion value .sigma.1 to the
dispersion value .sigma.2 of less than 1.2, and therefore, the
strength is weak. Also, it has a high electric resistance as a
transparent conductive layer and the values of the electric
resistance vary widely.
[0059] Next, the conductive fine particles-containing layer formed
is compressed to obtain a compressed layer of the conductive fine
particles. By the compression, the situation as if the conductive
fine particles are embedded in the transparent support is realized
and the ratio (.sigma.1/.sigma.2) of the dispersion value .sigma.1
to the dispersion value .sigma.2 becomes 1.2 or more. Thereby, the
decrease of the electric resistance and the enhancement of the film
strength are achieved. That is, the contacting points among the
conductive fine particles are increased by the compression and thus
the contacting area is increased. Accordingly, the electric
resistance decreases and the coating film is strengthened. Since
the fine particles have naturally a nature of being apt to
agglomerate, the compression affords a strong film. Also, the
compression decreases haze degree.
[0060] The compression is preferably carried out under a
compressing force of 44 N/mm.sup.2 or more. When the force is less
than 44 N/cm.sup.2, the conductive fine particles-containing layer
cannot be compressed sufficiently and thus it is difficult to
obtain a transparent conductive layer excellent in conductivity.
The compressing force of 180 N/mm.sup.2 or more is more preferred
for the compression. A transparent conductive layer having superior
conductivity is obtained by higher compressing force, thereby the
strength of the transparent conductive layer is enhanced and the
adhesion to the transparent support is strengthened. Since a higher
compressing force requires an increased pressure resistance of the
apparatus, the compressing force up to 1000 N/mm.sup.2 is generally
suitable.
[0061] Furthermore, it is preferred to carry out the compression at
around ordinary temperature (15 to 40.degree. C.). When the
compression is carried out under heating conditions (hot pressing),
there occurs inconvenience that the resin film is expanded under an
increased compressing pressure.
[0062] The compressing means is not particularly limited, and sheet
pressing, roll pressing, and the like can be applied. The
compression is preferably carried out using a roll-pressing
machine. The roll pressing is a process wherein a film to be
compressed is compressed by interposing it between two rolls, and
the rolls are rotated. The roll pressing is suitable because a high
pressure can be applied evenly and productivity is high owing to
the capability of roll-to-roll production.
[0063] The roll temperature of the roll-pressing machine is
preferably ordinary temperature. Under a heated atmosphere or at
the compression wherein the rolls are heated (hot-pressing), there
occurs inconvenience that the resin film is expanded under an
increased compressing pressure. When the compressing pressure is
reduced in order to prevent the expansion of the resin film under
heating, the mechanical strength of the transparent conductive
layer decreases and the electric resistance increases. In the case
that it is desired to reduce the moisture attached to the fine
particle surface as far as possible, the atmosphere may be heated
for lowering the relative humidity of the atmosphere but the
temperature should be within the range where the film is not easily
expanded. In general, the range is equal to or lower than glass
transition temperature (secondary transition temperature). In
consideration of the variation of humidity, the temperature may be
set at a temperature slightly higher than the temperature at which
required humidity is attained. In the case of continuous
compression using a roll-pressing machine, it is preferable to
regulate the temperature so that the roll temperature does not
increase owing to heat generation. By the way, the glass transition
temperature of a resin film is determined through measuring dynamic
viscoelasticity, and indicates the temperature at which mechanical
loss of primary dispersion reaches its peak. For example, the glass
transition temperature of PET film is about 110.degree. C.
[0064] A metal roll is suitable for the roll of the roll-pressing
machine since a strong pressure can be applied. In addition, it is
preferable to form a hard film on the surface of the roll because
the conductive fine particles may be transcribed to the roll at the
compressing when the roll surface is soft.
[0065] As mentioned above, the transparent conductive film of the
present invention comprising a transparent conductive layer is
obtained by forming a compressed layer of the conductive fine
particles. The thickness of the transparent conductive layer varies
depending on the applications, but may be about 0.1 to 10 .mu.m, as
mentioned above. Furthermore, for obtaining a thick transparent
conductive layer of about 10 .mu.m, a series of the operations of
applying, drying and compressing of the dispersion of the
conductive fine particles may be repeated. By the way, in the case
that a functional layer where the same functional layers are
laminated is obtained by repeating the same operations, the
outermost surface of the lamination is regarded as the surface to
be measured. Also, in the case that a functional layer where
different functional layers are laminated is obtained, the
outermost surface of the lamination is regarded as the surface to
be measured.
[0066] The transparent conductive film of the present invention
thus obtained exhibits an excellent conductivity at its transparent
conductive layer, has practically enough film strength although it
is formed by no use of a conventional large amount of binder resin,
and is excellent in adhesiveness to the transparent support.
[0067] In the above embodiment, a transparent conductive film is
mentioned as a functional film, but the functional film of the
present invention includes, without limitation, films having
various functions such as a conductive film, a magnetic film, a
ferromagnetic film, a dielectric film, a ferroelectric film, an
electrochromic film, an electroluminescence film, an insulating
film, a light-absorption film, a light-selective-absorption film, a
reflection film, an antireflection film, a catalyst film, and a
photocatalyst film. Therefore, in the present invention, functional
fine particles constituting the above aimed film are used. The
functional fine particles are not particularly limited, and mainly
inorganic fine particles having a cohesive force are used. In any
functional film of the present invention, a functional layer having
an enough mechanical strength is obtained and also problems caused
by a binder resin in the conventional coating method using a large
amount of the binder resin can be solved. As a result, an enhanced
objective function is exhibited.
[0068] Other than the above transparent conductive film, in the
ferromagnetic film, for example, oxide-type magnetic powder such as
.gamma.-Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, Co--FeO.sub.x, and Ba
ferrite; ferromagnetic alloy powder mainly composed of
ferromagnetic metal element(s) such as .alpha.-Fe, Fe--Co, Fe--Ni,
Fe--Co--Ni, Co, and Co--Ni; and the like are used, and the
saturation magnetic flux density of a magnetic coated film which is
a functional layer is enhanced.
[0069] In the dielectric film and ferroelectric film, fine
particles of dielectric substances or ferroelectric substances such
as magnesium titanate, barium titanate, strontium titanate, lead
titanate, lead zirconate titanate (PZT), lead zirconate,
lanthanum-added lead zirconate titanate (PLZT), magnesium silicate,
and lead-containing perovskite compounds are used. In the
dielectric film and ferroelectric film of the present invention,
the improvement of dielectric properties or ferroelectric
properties is obtained.
[0070] Furthermore, in the metal oxide films expressing various
functions, fine particles of metal oxides such as iron oxide
(Fe.sub.2O.sub.3), silicon oxide (SiO.sub.2), aluminum oxide
(Al.sub.2O.sub.3), titanium dioxide (TiO.sub.2), titanium oxide
(TiO), zinc oxide (ZnO), zirconium oxide (ZrO.sub.2), and tungsten
oxide (WO.sub.3) are used. In the metal oxide films of the present
invention, each function is improved because of increased packing
density of the metal oxide in each functional layer. For example,
in the case of using SiO.sub.2 or Al.sub.2O.sub.3 on which a
catalyst is supported, a porous catalyst film having a practical
strength is obtained. In the case of using TiO.sub.2, a
photocatalytic function is improved. Further, in the case of using
WO.sub.3, coloring action is improved in an electrochromic display
device.
[0071] Moreover, in the electroluminescence film, zinc sulfide
(ZnS) fine particles are used. The electroluminescence film of the
present invention can be an inexpensive film obtainable by coating
method.
[0072] The particle size, r, of the functional fine particles
varies depending on the applications, for example, required degree
of scattering and the like, and also depends on the shape of the
particles, but in general, average primary particle size, r is 10
.mu.m or less, preferably 1.0 .mu.m or less, more preferably from 5
nm to 100 nm.
[0073] The following will explain the present invention in detail
with reference to Examples, but the invention is not limited these
Examples.
EXAMPLE 1
[0074] First, 300 parts by weight of ethanol was added to 100 parts
by weight of ATO fine particles having average primary particle
size of 20 nm (SN-100P manufactured by Ishihara Sangyo K.K.), and
the particles were dispersed in a dispersing machine using zirconia
beads as media to prepare a conductive coating composition.
[0075] Next, the above conductive coating composition was applied
onto a PET film (a thickness of 50 .mu.m) using a bar coater and
dried at 50.degree. C. Hereinafter, the resulting film was referred
to as a pre-compression ATO film. The thickness of the
ATO-containing coated film was 2.2 .mu.m.
[0076] Then, the pre-compression ATO film was interposed between
metal rolls (the roll surfaces were subjected to a hard
chromium-plating treatment), and was compressed by rotating the
rolls at room temperature (23.degree. C.) at a feeding rate of 5
m/minute. The compressing pressures per unit area at the
compressing step were set differently as shown in following Table
1. Transparent conductive films (Samples 1 to 6) comprising each
transparent conductive layer were obtained by compressing the ATO
films in such a manner.
[0077] Moreover, 100 parts by weight of the same ATO powder as
above was added to a resin solution obtained by dissolving 100
parts by weight of an acrylic resin solution MT408-42 (non-volatile
component concentration of 50%) manufactured by Taisei Kako K.K. as
a resin into 400 parts by weight of a methyl ethyl
ketone/toluene/cyclohexanone (1:1:1) mixed solution, and the powder
was dispersed in a dispersing machine using zirconia beads as media
to prepare a conductive coating composition. Using the conductive
coating composition, a transparent conductive film (Sample 7) was
obtained in a similar manner to the above transparent conductive
films (Samples 1 to 6). However, the compressing pressure per unit
area at the compressing step was set as shown in following Table
1.
[0078] Furthermore, a transparent conductive film (Sample 8) was
obtained in a similar manner to the above transparent conductive
film (Sample 3: no resin was used) with the exception that a
silicon resin hard coat material of a thickness of 3 .mu.m
(Tosguard 510 manufactured by GE Toshiba silicone K.K.) placed on
the above PET film was used as a transparent support.
[0079] For the eight kinds of the transparent conductive films
(Samples 1 to 8), the thickness of the transparent conductive layer
after the compression was measured, and the ratio
(.sigma.1/.sigma.2) of the dispersion value al to the dispersion
value .sigma.2 was measured on each transparent conductive layer
according to the following measuring method. The results are shown
in following Table 1.
[0080] In addition, the surface electric resistance and haze were
measured according to the following measuring methods, and the
results are shown in following Table 1. Furthermore, for evaluating
the adhesiveness between the PET film and the transparent
conductive layer and the strength of the transparent conductive
layer, a 90.degree. peel test was carried out according to the
following method, and the results are shown in following Table
1.
[0081] Measuring Method of the Ratio (.sigma.1/.sigma.2)
[0082] A squared tracing paper is placed on the cross sectional
photograph of 100 thousand magnifications of the transparent
conductive film without deviation, and the end surfaces at which
the conductive fine particles at the interface side and at the
surface side of the transparent conductive layer are aligned are
each traced to obtain lines L1 and L2 showing aligning states of
the conductive fine particles. By the way, at the part where the
conductive fine particles are apparently lacked, a line segment is
obtained by extrapolating from both side of the lacking part. Then,
base line B1 and B2 are drawn at about 1 cm apart from each of the
lines L1 and L2 showing aligning states of the conductive fine
particles. And, the distances between the base line B1 and the line
L1 and the distances between the base line B2 and the line L2 are
each measured at an interval of 2 mm (the measuring length is 10
cm). The average squares of the differences between the average
value of the measured values and each measured value are each
defined as the dispersion values .sigma.1, .sigma.2, and the ratio
(.sigma.1/.sigma.2) is calculated.
[0083] Measurement of Surface Electric Resistance
[0084] The transparent conductive film where a transparent
conductive layer is formed was cut into a piece having a size of 50
mm.times.50 mm, and the electric resistance is measured by applying
terminal bars of a circuit tester to two corner points which are
diagonally positioned.
[0085] Measurement of Haze
[0086] It is measured using a haze meter (TC-H3 DPK model
manufactured by Tokyo Densyoku K.K.).
[0087] 90.degree. Peel test
[0088] A double-stick tape is installed to the surface of the PET
film of the transparent conductive film opposite to the surface to
which the transparent conductive layer is formed. The resulting
film is cut into a piece having a size of 25 mm.times.100 mm to be
a sample, which is then adhered to a stainless plate. Successively,
a cellophane tape is installed at both sides of the test sample (at
the sides having a length of 25 mm) so as to prevent peeling of the
test sample. Thereafter, a cellophane tape (width 12 mm, No. 29
manufactured by Nitto Denko K.K.) is installed to the surface of
the transparent conductive layer of the test sample so as to be
parallel to the long side of the test sample. The length of the
cellophane tape installed to the test sample is 50 mm. Then, the
uninstalled end of the cellophane tape is fixed to a chuck and the
sample is set so that the angle between the installed surface and
uninstalled surface of the cellophane tape becomes 90.degree.. The
cellophane tape is peeled off by pulling the tape at a rate of 100
mm/minute. At that time, the stainless steel plate is moved at the
same rate as the peeling rate of the cellophane tape so that the
angle between the uninstalled surface of the cellophane tape and
the surface of the test sample is kept 90 .degree.. After the test,
the conditions of the coated film is examined to be evaluated in
accordance with the following evaluation standard.
[0089] .smallcircle.: the coated film is not broken and no peeling
from the PET film is observed.
[0090] .times.: the coated film is broken and part of the coated
film is attached to the cellophane tape.
1TABLE 1 Trans- Thickness of Com- parent transparent pressing
90.degree. conductive conductive pressure .sigma.1/ Electric Haze
peel film layer (.mu.m) (N/mm.sup.2) .sigma.2 resistance (%) test
Sample 1 1.7 56 1.25 254 k.OMEGA. 4.2 .largecircle. Sample 2 1.5
157 1.34 112 k.OMEGA. 3.5 .largecircle. Sample 3 1.4 347 1.51 58
K.OMEGA. 3.1 .largecircle. Sample 4 1.3 500 1.72 52 k.OMEGA. 2.9
.largecircle. Sample 5 1.2 1000 1.83 45 k.OMEGA. 2.6 .largecircle.
Sample 6 1.9 13 1.05 845 k.OMEGA. 5.2 X Sample 7 1.4 330 0.98 7.2
M.OMEGA. 2.3 .largecircle. Sample 8 1.3 347 0.97 57 k.OMEGA. 3.2
X
[0091] As shown in Table 1, it was confirmed that the transparent
conductive films of the present invention comprising a transparent
conductive layer having the ratio (.sigma.1/.sigma.2) of the
dispersion values .sigma.1, .sigma.2 of 1.2 to 1.85 (Samples 1 to
5) had all a sufficiently low electric resistance and a low haze,
i.e., a sufficient transparency. Also, these transparent conductive
films exhibited a good adhesiveness of the transparent conductive
layer to the PET film although the transparent conductive layer
contained no resin.
[0092] To the contrary, the transparent conductive films comprising
the transparent conductive layer having the ratio
(.sigma.1/.sigma.2) of the dispersion values .sigma.1, .sigma.2 of
less than 1.2 (Samples 6, 8) exhibited a bad adhesiveness of the
transparent conductive layer to the PET film irrespective of the
electric resistance of the transparent conductive layer.
[0093] Moreover, since the transparent conductive film comprising
the transparent conductive layer having the ratio
(.sigma.1/.sigma.2) of the dispersion values .sigma.1, .sigma.2 of
less than 1.2 (Sample 7) contained a large amount of the resin in
the transparent conductive layer, the adhesiveness of the
transparent conductive layer to the PET film was good but the
electric resistance of the transparent conductive layer was
high.
EXAMPLE 2
[0094] First, 300 parts by weight of methanol was added to 100
parts by weight of ITO fine particles having average primary
particle size of 20 nm (SUFP-HX manufactured by Sumitomo Metal
Mining Co. Ltd.), and the particles were dispersed in a dispersing
machine using zirconia beads as media to prepare a conductive
coating composition.
[0095] Next, the above conductive coating composition was applied
onto a PET film having a thickness of 50 .mu.m using a bar coater
and dried at 50.degree. C. Hereinafter, the resulting film was
referred to as a pre-compression ITO film. The thickness of the
ITO-containing coated film was 1.9 .mu.m.
[0096] Then, the pre-compression ITO film was interposed between
metal rolls (the roll surfaces were subjected to a hard
chromium-plating treatment), and was compressed by rotating the
rolls at room temperature (23.degree. C.) at a feeding rate of 5
m/minute. The compressing pressures per unit area at the
compressing step were set differently as shown in following Table
2. Transparent conductive films (Samples I to VI comprising each
transparent conductive layer were obtained by compressing the ITO
films in such a manner.
[0097] Moreover, 100 parts by weight of the same ITO powder as
above was added to a resin solution obtained by dissolving 100
parts by weight of an acrylic resin solution MT408-42 (non-volatile
component concentration of 50%) manufactured by Taisei Kako K.K. as
a resin into 400 parts by weight of a methyl ethyl
ketone/toluene/cyclohexanone (1:1:1) mixed solution, and the powder
was dispersed in a dispersing machine using zirconia beads as media
to prepare a conductive coating composition. Using the conductive
coating composition, a transparent conductive film (Sample VII) was
obtained in a similar manner to the above transparent conductive
films (Samples I to VI). However, the compressing pressure per unit
area at the compressing step was set as shown in following Table
2.
[0098] Furthermore, a transparent conductive film (Sample VIII) was
obtained in a similar manner to the above transparent conductive
film (Sample III: no resin was used) with the exception that a
silicon resin hard coat material of a thickness of 3 .mu.m
(Tosguard 510 manufactured by GE. Toshiba silicone K.K.) placed on
the above PET film was used as a transparent support.
[0099] For the transparent conductive films (Samples I to VIII),
the thickness of the transparent conductive layer, the ratio
(.sigma.1/.sigma.2) of the dispersion values .sigma.1, .sigma.2,
surface electric resistance, and haze were measured in a similar
manner to Example 1 and the results are shown in following Table 2.
Furthermore, a 90.degree. peel test was carried out in a similar
manner to Example 1, and the results are shown in following Table
2.
2TABLE 2 Trans- Thickness Com- parent of transparent pressing
90.degree. conductive conductive pressure .sigma.1/ Electric Haze
peel film layer (.mu.m) (N/mm.sup.2) .sigma.2 resistance (%) test
Sample I 1.4 56 1.23 4.8 k.OMEGA. 3.3 .largecircle. Sample II 1.3
157 1.33 3.2 k.OMEGA. 2.7 .largecircle. Sample III 1.2 347 1.48 1.1
k.OMEGA. 2.2 .largecircle. Sample IV 1.2 500 1.72 0.9 k.OMEGA. 2.0
.largecircle. Sample V 1.1 1000 1.81 0.8 k.OMEGA. 1.8 .largecircle.
Sample VI 1.7 13 1.02 18.2 k.OMEGA. 4.3 X Sample 1.3 330 0.98 160
k.OMEGA. 2.1 .largecircle. VII Sample 1.2 347 0.96 1.0 k.OMEGA. 2.2
X VIII
[0100] As shown in Table 2, it was confirmed that the transparent
conductive films of the present invention comprising a transparent
conductive layer having the ratio (.sigma.1/.sigma.2) of the
dispersion values .sigma.1, .sigma.2 of 1.2 to 1.85 (Samples I to
V) had all a sufficiently low electric resistance and a low haze,
i.e., a sufficient transparency. Also, these transparent conductive
films exhibited a good adhesiveness of the transparent conductive
layer to the transparent support although the transparent
conductive layer contained no resin.
[0101] To the contrary, the transparent conductive films comprising
the transparent conductive layer having the ratio
(.sigma.1/.sigma.2) of the dispersion values .sigma.1, .sigma.2 of
less than 1.2 (Samples VI, VIII) exhibited a bad adhesiveness of
the transparent conductive layer to the transparent support.
[0102] Moreover, since the transparent conductive film comprising
the transparent conductive layer having the ratio
(.sigma.1/.sigma.2) of the dispersion values .sigma.1, .sigma.2 of
less than 1.2 (Sample VII) contained a large amount of a resin in
the transparent conductive layer, the adhesiveness of the
transparent conductive layer toward the PET film was good but the
electric resistance of the transparent conductive layer was
high.
* * * * *